Tesla quietly revealed this week that it’s been delivering its Model S electric sedans more slowly than expected. Tesla says it’s about five weeks behind its previously announced production schedule, which means Tesla had to cut its revenue guidance for the year and will deliver fewer Model S cars to customers than expected in 2012. The rest of 2012 could be a difficult time for the auto maker as it tries to ramp up its production and deliver its vehicles on time.

Another indicator that Tesla needs considerable funds in the short term: Tesla asked its first several thousand customers on its reservation list (it’s had 13,000 reservation holders in total) to configure their cars for delivery (basically commit to buying them) or risk losing their production slot. Tesla doesn’t record revenue until the Model S is actually delivered.

As a result of Tesla sending that note to reservation holders, about 1,000 customers cancelled their reservations. Tesla said while they brought in 2,600 reservations for the Model S during the third quarter, Tesla adjusted that down to 1,600 net reservations because of the cancellations. Tesla says in the filing: “We expect the cancellation rate to decrease after we work through the older reservations on our list and there is less of a gap between a customer placing a reservation, configuring the car and receiving delivery.”

As a result of the tight funds, Tesla has also adjusted its pay-back schedule for the loan from the U.S. Department of Energy. The company pushed back a payment from October 2012 to February 2013, and will accelerate its payback schedule after that in 2013.

Tesla’s stock rose 3.72 percent on the news of the public offering. This week Tesla also revealed its solar-powered Superchargers, which will power a Model S in under 30 minutes, and said it has already installed six of these through the California area. Tesla plans to build out these chargers throughout the U.S. and act as a sort electric car infrastructure provider.